Bulletin of the American Physical Society
2012 Fall Meeting of the APS Division of Nuclear Physics
Volume 57, Number 9
Wednesday–Saturday, October 24–27, 2012; Newport Beach, California
Session JD: Nuclear Structure IV |
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Chair: Noemie Koller, Rutgers University Room: Patio |
Friday, October 26, 2012 10:30AM - 10:42AM |
JD.00001: Nuclear structure of $^{106}$Pd and $^{106}$Cd from the (n,n$^{\prime}\gamma$) reaction F.M. Prados-Est\'{e}vez, A. Chakraborty, E.E. Peters, M.G. Mynk, D. Bandyopadhyay, N. Boukharouba, S.N. Choudry, B.P. Crider, A. Kumar, S. Lesher, C.J. McKay, M.T. McEllistrem, S. Mukhopadhyay, J.N. Orce, M. Scheck, S.W. Yates, P.E Garrett, S. Hicks, J.R. Vanhoy, J.L. Wood Quadrupole shape vibrations are considered to be fundamental degrees of freedom of nuclei. Several candidates in the $_{48}$Cd and $_{46}$Pd region have been proposed as examples of good quadrupole shape vibrators; however, in recent studies of the heavy stable Cd nuclei, serious discrepancies from the vibrational decay pattern were found, suggesting a breakdown of the quadrupole vibrational picture. New studies of the $_{48}$Cd and $_{46}$Pd isotopes promise to bring new insights into the role of vibrations in nuclei. The low-lying states of $^{106}$Pd and $^{106}$Cd have been studied with the (n,n$^{\prime}\gamma$) reaction at the University of Kentucky 7-MV Van de Graaff accelerator facility. Gamma-ray excitation functions, angular distributions, and coincidence data ($^{106}$Pd) were used to characterize the excited states up to $\sim$4.0 MeV in each nucleus. [Preview Abstract] |
Friday, October 26, 2012 10:42AM - 10:54AM |
JD.00002: Gamma-ray cascade transitions in $^{112}$Cd and $^{114}$Cd following capture of epithermal neutrons G. Rusev, M. Jandel, T.A. Bredeweg, T.N. Taddeucci, J.L. Ullmann, M. Krticka Investigation of the properties of the $\gamma$-ray transitions in the cadmium isotopes are of importance for nuclear structure and applied physics due to the high cross section for capture of thermal neutrons by $^{111}$Cd and $^{113}$Cd. We report results from a neutron-capture experiment on $^{\rm nat}$Cd carried out at LANL's LANSCE using the $4\pi$ BaF$_2$ DANCE array. Isolated resonances with known spins were selected to study the $\gamma$-ray cascade transitions in $^{112}$Cd and $^{114}$Cd. Experimental results are compared with predictions from the code \texttt{DICEBOX} to determine the optimal $\gamma$-ray strength function that reproduces these cascade transitions. [Preview Abstract] |
Friday, October 26, 2012 10:54AM - 11:06AM |
JD.00003: Disappearance of Z=120 {\&} 126 magicity and presence of hyper deformations in superheavy nuclei M.M. Sharma, A.R. Farhan Conventional wisdom has it that Z=120 and especially Z=126 are predicted to be magic numbers for extreme superheavy nuclei. We have undertaken a study of structure of superheavy nuclei in the region of Z=120 to Z=126 within the framework of the deformed relativistic Hartree-Bogoliubov (DRHB) approach. Nuclei in this region entail a large density of states and are thus susceptible to a coupling to the continuum especially those which are close to being proton unbound. The DRHB approach which takes into account the coupling to the continuum is suitable for nuclei in the end of the periodic table. Additionally, the pairing in this approach is included within the Bogoliubov quasi-particle scheme, which takes into account the shell gap at the Fermi surface appropriately. Using the successful Lagrangian model NL-SV1 [1] based upon the vector self-coupling of $\omega $-meson, it is shown that the perceived shell gaps at Z=120 and Z=126 disappear, thus making these proton numbers as non-magic. It is also shown that due to very large Coulomb force acting in these nuclei which are virtually at the end of the periodic table, stability to the nuclei in this region is brought about by extremely large elongated shapes with $\beta _{2 } \sim $ 0.70-0.80. Consequences on formation of superheavy nuclei in this region will be discussed. [Preview Abstract] |
Friday, October 26, 2012 11:06AM - 11:18AM |
JD.00004: Magnetic Moments measurement and rare isotope beams: one example $^{126}$Sn Gerfried Kumbartzki, Noemie Benczer-Koller An assessment of the current state of measurements of magnetic moments of ps excited states with low intensity rare isotope beams will be given. $^{126}$Sn was our last experiment before HRIBF/Oak Ridge ceased operation. Results of only a few experiments using the transient field technique and/or recoil in vacuum attenuation have been published. Each experiment posed special challenges and required specific modifications to the setup. The challenges and limitations learned and an outlook for future experiments will be presented. [Preview Abstract] |
Friday, October 26, 2012 11:18AM - 11:30AM |
JD.00005: Neutron Transfer Reactions with $^{126,128}$Sn Rare Isotope Beams B. Manning, J.A. Cizewski, R.L. Kozub, S.H. Ahn, D.W. Bardayan, K.Y. Chae, K.A. Chipps, M.E. Howard, K.L. Jones, J.F. Liang, M. Matos, C.D. Nesaraja, P.D. O'Malley, S.D. Pain, W.A. Peters, S.T. Pittman, A. Ratkiewicz, K.T. Schmitt, D. Shapira, M.S. Smith Neutron transfer reactions with $^{132}$Sn beams have identified robust single-neutron excitations in $^{133}$Sn above the N=82 shell closure. A similar pattern has been observed in $^{131}$Sn, with potential implications for r-process abundances. To extend the systematics of single-neutron excitations in neutron-rich Sn nuclei, the (d,p) reactions has been studied with beams of $^{126,128}$Sn. Measurements were performed at the HRIBF at ORNL with arrays of charged particle detectors including the Super ORRUBA highly-segmented silicon detector array. Preliminary results from these studies, and in comparison with measurements with stable $^{124}$Sn and earlier $^{130,132}$Sn beams will be presented. [Preview Abstract] |
Friday, October 26, 2012 11:30AM - 11:42AM |
JD.00006: Search for Transverse Wobbling in $^{135}$Pr J.T. Matta, U. Garg, S. Frauendorf, A.D. Ayangeakaa, D. Patel, S. Zhu, M. Carpenter, T. Lauritsen, F. Kondev, D. Seweryniak, C. Petrache, R. Palit, S. Saha, J. Sethi, T. Trivedi, S. Mukhopadhyay, S. Ray, R. Raut, S. Ghugre, A. Sinha Nuclear wobbling has previously been observed in $^{161,163,165,167}$Lu and in $^{167}$Ta. In these cases the inter-band transitions display the expected $\Delta$I=1, E2 nature, but the wobbling frequency, ($\Delta E=\hbar\omega_{w}I=E(I,\alpha=\frac{1}{2})-(E(I-1,\alpha=-\frac{1}{2}) +E(I+1,\alpha=-\frac{1}{2}))/2 $), decreases with increasing spin. This remains an open theoretical problem as the Hamiltonian suggests increasing frequency with spin. Here the concept of a ``transverse wobbler'' provides an explanation. In this the angular momentum wobbles about the short axis and at a critical frequency this motion becomes unstable and the frequency becomes zero. A previous level scheme of $^{135}$Pr showed two h$_{\frac{11}{2}}$ bands whose properties seemed to exhibit the traits expected of a transverse wobbler. Results from investigations of $^{135}$Pr at both Gammasphere and INGA will be presented. [Preview Abstract] |
Friday, October 26, 2012 11:42AM - 11:54AM |
JD.00007: A search for 2-photon emission from the 662 keV state in $^{137}$Ba using Gammasphere C.J. Lister, E.A. McCutchan, K. Moran, S. Zhu, M.P. Carpenter, J.P. Greene, J.D. Millener, R.J. Sutter, D.E. Alburger Two photon decays from excited nuclear states provide an interesting test both of QED and nuclear structure. It has been extensively studied for cases where one photon decay is forbidden [1]. Two photon decay in direct competition with the first order process has never been convincingly demonstrated. Nonetheless, observation of this decay will provide additional challenging tests for experiment and theory. The $^{137}$Ba case is particularly interesting as the decay has high multipolarity, M4, so the 2-photon process can have contributions from both quadrupole-quadrupole and dipole-octupole multipolarities. Gammasphere is the perfect tool for this investigation, having good energy resolution, good efficiency, good coverage of angles, and sufficient granularity to minimize pile-up and count-rate difficulties. A short test experiment showed the power of Gammasphere and the dauntingly high Compton scattering background that need suppression. However, new calculations and new measurements from Brookhaven suggest that the two photon branch is $\sim $2 x 10$^{-6}$ and should be measurable. This work was supported by DOE contracts, DE-FG02-94ER40848, DE-AC02-06CH11357 and ~DE-AC02-98CH10946.\\[4pt] [1] J. Kramp, et. al, Nucl. Phys. A474 (1987) 412 [Preview Abstract] |
Friday, October 26, 2012 11:54AM - 12:06PM |
JD.00008: Testing Shell Stabilization at N = 80; $g$ factor of the 2$^{+}_{1}$ state in $^{138}$Ce F. Naqvi, V. Werner, T. Ahn, G. Ilie, N. Cooper, D. Radeck, M.P. Carpenter, C.J. Chiara, F. Kondev, T. Lauritsen, C.J. Lister, D. Seweryniak, S. Zhu The study of observed mixed symmetry states in N = 80 isotones, namely $^{134}$Xe, $^{136}$Ba and $^{138}$Ce manifest a large effect of single-particle structure on the evolution of these collective excitations. The observed fragmentation of $M1$ transition strength between the (2$_{1,ms}^{+}$) state and the ($2_{1,fs}^{+}$) state in $^{138}$Ce and the largely unfragmented strength in $^{134}$Xe and $^{136}$Ba was attributed to the presence of a $\pi g_{7/2}$ subshell closure at $Z=58$. To prove the validity of this proposed concept of shell stabilization, the $g$ factor of the 2$^{+}_{1}$ in $^{138}$Ce was measured. The low-lying excited states in $^{138}$Ce were populated via inverse Coulomb excitation at ATLAS, ANL. To measure the $g$ factor, the recoil into vacuum technique was used and attenuation of the angular distribution of emitted 2$^{+}_{1}\rightarrow0^{+}\gamma$ rays was measured. The results of the ongoing analysis will be presented providing a constraint on the single-particle wavefunctions contributing to the collective states in the N = 80 isotones and guide theory in developing a consistent and predictive picture of the underlying single-particle dynamics. [Preview Abstract] |
Friday, October 26, 2012 12:06PM - 12:18PM |
JD.00009: First $\beta$-decay study with CARIBU and Gammasphere: $^{142,144}$Cs to $^{142,144}$Ba S. Zhu, M. Alcorta, P.F. Bertone, M.P. Carpenter, C.R. Hoffman, R.V.F. Janssens, F.G. Kondev, T. Lauritsen, C.J. Lister, R. Pardo, A.M. Rogers, G. Savard, D. Seweryniak, R. Vondrasek As part of the commissioning of the CARIBU facility at ATLAS, beams of $^{142}$Cs and $^{144}$Cs ions from CARIBU was charge bred and, subsequently, accelerated to $\sim$6 MeV/A by ATLAS before being transported to the target location of Gammasphere. The $^{142}$Cs beam was implanted in a Pb foil with the rate of $10^3$ ions/s for 16 hours and $\gamma$ radiation following $\beta$ decay (T$_{1/2}$ = 1.68s) was detected by the 101 Compton-suppressed germanium detectors of the Gammasphere array. The power of the CARIBU-Gammasphere combination for $\beta$-decay investigations was demonstrated. The $^{142}$Ba level scheme was considerably expanded: 215 $\gamma$ transitions have been identified and placed into an expanded level scheme with 71 states. Furthermore, a large number of spin-parity assignments were made based on the measured angular correlations. High-precision {\it log ft} values were determined as well. The data provide important new information about the nature of low-spin excitations in this nucleus. In particular, new information is obtained about the strength of octupole correlations and the nature of other low-lying excitations. [Preview Abstract] |
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